1. Field of the Invention
The present invention pertains to surgical penetrating instruments for accessing cavities within the body and, more particularly, to such penetrating instruments formed of trocars having solid, tissue penetrating, sharp tips and safety shields surrounding the trocars for preventing tissue from contacting the sharp tips after entry into body cavities.
2. Discussion of the Prior Art
Trocars are commonly used for accessing cavities within the body and establishing an endoscopic portal for various procedures to be performed by least invasive surgery. Portal sleeves or cannulas are normally disposed around the trocars to be positioned upon penetration into the cavity by the trocar. Trocars include a sharp tissue penetrating pyramidal distal end or tip to pierce or penetrate tissue forming the cavity wall, and the force required to penetrate the cavity wall is dependent upon the type and thickness of the tissue of the wall. Once the wall is penetrated, it is desirable to prevent the sharp tip of the trocar from inadvertently contacting tissue in or forming the cavity, and a particular problem exists where substantial force is required to penetrate the cavity wall in that, once penetration is achieved, the lack of tissue resistance can result in the sharp trocar tip traveling too far into the cavity and injuring adjacent tissue. Safety trocars having a spring-biased protective shield disposed between an outer portal sleeve and an inner trocar are marketed by Ethicon, Inc. as the Endopath and by United States Surgical Corporation as the Surgiport, and U.S. Pat. No. 4,535,773 to Yoon, No. 4,601,710 to Moll and No. 4,654,030 to Moll et al are exemplary of such safety trocars.
A disadvantage of prior art safety trocars is that the safety shields cannot be locked in an extended position protecting the sharp trocar tips for safety in handling and use. A further disadvantage of prior art safety trocars is that the safety shields cannot be selectively retracted to expose the sharp trocar tips without a force being applied to the safety shields with tissue contact. Accordingly, the sharp trocar tips in prior art safety trocars cannot be effectively used in further penetration or treatment of tissue after a cavity wall is initially penetrated; and, therefore, the types of surgical procedures that can be performed with prior art safety trocars are thusly limited. Another disadvantage of prior art safety trocars is that the protective shields form an irregular surface or profile with the trocars resulting in increased resistance from tissue during penetration of a cavity wall, greater trauma and damage to tissue and possible jamming and trapping of tissue between the trocars and the safety shields.